The present invention is related to capacitive discharge ignitions, and, in particular, to capacitive discharge ignitions which provide a spark of long duration.
Capacitive discharge ignitions (CDIs) are, in general, well-known. Examples of capacitive discharge ignitions are described in the following U.S. Pat. No. 4,074,669, issued to Cavil, Feb. 1978; U.S. Pat. No. 4,056,088, issued to Carmichael, Nov. 1977; U.S. Pat. No. 4,213,436, issued to Burson, July 1980; U.S. Pat. No. 3,955,550, issued to Carlsson, May 1976; U.S. Pat. No. 3,828,754, issued to Carlsson, Aug. 1974; U.S. Pat. No. 3,358,665, issued to Carmichael et al, Dec. 1967; U.S. Pat. No. 3,667,441, issued to Cavil, June 1972; U.S. Pat. No. 3,747,649, issued to Densow et al, July 1973; U.S. Pat. No. 3,490,426, issued to Farr, Jan. 1970; U.S. Pat. No. 3,517,655, issued to Jaulmes, June 1970; U.S. Pat. No. 3,720,194, issued to Mallory, Jr., Mar. 1973; U.S. Pat. No. Re. 27,477, issued to Piteo, Sept. 1972; U.S. Pat No. 3,835,830, issued to Shepherd, Sept. 1974; U.S. Pat. No. 3,598,098, issued to Sohner, Aug. 1971; and U.S. Pat. No. 3,461,851, issued to Stephens, Aug. 1969.
In general, such capacitive discharge ignition systems include a charge storage mechanism, such as a capacitor, a step-up transformer with the secondary thereof connected to a spark ignition device, e.g., spark plug, and a mechanism for controllably charging the capacitor and discharging the capacitor through the primary coil of the transformer in timed relation with the cooperating engine operation. Typically, a charge coil magnetically interacts with a rotor or flywheel rotated in synchronism with motor operation. A switching device, such as a silicon-controlled rectifier (SCR), is provided to controllably complete a discharge path from the capacitor through the transformer primary coil. The SCR, in turn, is triggered by a pulse generated in timed relation to the motor operation. The trigger pulse is typically generated either by interaction of a separate inductive trigger coil with the rotor, or by reversal of polarity of the voltage induced in the charging coil or similar use of the primary coil.
Various of the CDI systems utilize a separate triggering coil magnetically isolated from the charge coil. See, e.g., U.S. Pat. No. 3,598,098 to Sohner et al. Other CDI systems, such as those described in the aforesaid U.S. Pat. No. 3,667,441 to Cavil, U.S. Pat. No. 3,747,649 to Densow et al, and U.S. Pat. No. 4,074,669 to Cavil et al, employ separate trigger and charge coils (e.g., respective portions of a center tapped coil), which are disposed on the same magnetic core as the charge coil.
The discharge of the capacitor through the transformer primary coil induces a high voltage signal in the transformer secondary, which, if of sufficiently high magnitude, initiates a spark across the spark ignition device. More specifically, the voltage applied across a spark ignition device must be greater or equal to a predetermined characteristic "spark ionization potential" (voltage) in order to initiate the spark. Such ionization potentials are typically on the order of 10,000 volts (10 Kv). However, once the spark has been initiated, it is only necessary to maintain the gap voltage at a substantially lesser characteristic sustaining voltage, on the order of 500 volts, in order to sustain the spark.
It is desirable that a small CDI system generate sparks which manifest both high energy and long duration in order to facilitate starting the cooperating engine. Known induction magnetos provide such features, but tend to be more expensive and less reliable than CDI magnetos. The prior art CDI magnetos typically do not provide high energy and long duration sparks. In this regard, various of the prior art CDI systems employ multiple sparks generated in response to a damped oscillatory discharge of the capacitor through the transformer primary coil. See, e.g., the aforementioned U.S. Pat. No. 3,490,426 to Farr. More specifically, in multiple spark systems, the capacitor is initially charged with a first polarity, then discharged through the SCR. Discharging the capacitor through the SCR, however, recharges the capacitor with the opposite polarity. The capacitor, thus oppositely charged, is then discharged, and recharged to the initial polarity through a diode. Each discharge of the capacitor through the transformer primary coil induces a voltage in the transformer secondary, which, if of a sufficiently high magnitude, effects generation of a spark. The duration of the individual sparks, however, is only that of the discharge of the capacitor and thus extremely short in view of the low resistance of the discharge path.
It is also, in general, known to dispose the charge coil and transformer windings on a common magnetic core. In this regard, reference is made to the aforementioned U.S. Pat. No. 3,589,098 to Sohner et al and U.S. Pat. No. 4,056,088 to Carmichael. Carmichael teaches that by providing the ignition transformer coils on the same magnetic core as the charge/trigger winding (in systems not using a separate trigger coil), the primary winding of the ignition coil is energized not only by discharge of the capacitor, but also simultaneously by the magnetic field used to induce a charging current in the charge/trigger winding, and thus increased power can be supplied to the spark plug. However, such prior art systems have not provided an induced voltage in the transformer secondary of sufficiently high magnitude and in proper timed relation with the capacitive discharge to provide a sustaining voltage to the spark plug.
CDI systems have been proposed which provide for generation of a sustaining voltage to a spark device in timed relation to the ionization voltage. However, such devices have been relatively complex and costly, requiring an additional capacitor coupled to the secondary of the transformer. In this regard, reference is made to U.S. Pat. No. 3,835,830 to Shepherd.